Nick Raaum

I've thought  int the past alot along these lines, though ultimately I was led to conclude that a high volume low speed stirling or brayton style mechanical cycle was the most effective ways to accomplish this.  This example engine though illustrates the design in action http://www.solarheatengines.com/2012/01/10/tamera-video-of-sunvention-sunpulse-engine/  

That answer was more complicated than I desired though and I never pursued it.  What you are talking about is basically an evaporative engine.  The physics are actually a bit complicated.   You want to evaporate water with the lowest amount of energy and capture back a bit of that energy in gravitational potential energy.  To increase power output  for a given solar input you have two variables, one is the hight at which you are capturing condensate and the other is the amount of heat you put into the water to evaporate.   It is the second variable that makes things complicated, at high humidity or higher power inputs the latent heat needed to evaporate will begin to approach heat of vaporization or ~900 BTU/lbm if memory serves me.   In other words atmospheric changes will affect power output so significantly that one day your system may work well the next day humidity rises and the fish die, unless your system is ridicously oversized to account for it.

I think a good place to start would be to try to determine the minimum hydrostatic power needed to aerate the system and then work backwards to ensure the system can always meet that demand.  This will need to be based on local weather patterns and will necessarily entail developing enough thermal energy storage to keep system lifting water through longest and most humid periods of weather.

I think crunching some numbers on higher humidity levels out to make it apparent what the downsides of the low temperature evaporative cycle are.  I suspect you will need to design the system so that in worse case scenario you basically have enough energy stored up to be able to boil the minimum amount of aeratiuon water needed for days on end.  Say this is i don't know 1 gpm, that is at 70 deg  around 9,213 BTU/min energy input needed at a temp of up to 210 deg F (again this is for nearly saturated air) or 552,780BTU/hr.  roughly 377BTU/hr/ft^2 fall when sunny of which you might be able to capture 50% in well designed system leaving you with 2,909 ft^2 of energy capture needed to maintain flow through worse case conditions.  Wow that seems even worse than I thought perhaps I miscalculated...as its a square space roughly 54'x54' needed to be devoted to just solar collectors.

It could be that if your aquaponic system takes up a greenhouse space that big and you want the thing shaded that it might work out, but those collectors still cost a fair amount.  The inefficiencies  inherent in the cycle, even though a minimal amount of work output is needed still bite pretty hard at least when it gets very humid...if there was a way to avoid humidity and always have evaporative work be done without vaporizing then things would be very different, not sure how to do that though, other than to operate in a closed cycle.  In which case the optimal form of this engine would look like a super tall insulated loop.  Water would be heated to boiling point and then rise in the column to the point where ideally it condenses due to atmospheric temperature drop (thousands of feet) then falls back down through turbine to capture the energy.  At which point rather than expanding the steam against a gravitational field to do work it looks much more attractive and economical to expand through a piston against a load to gain the same efficiencies with a fraction of the material.  

Hi Marcin,
You may want to ping Marcos Buenijo on this forum https://permies.com/t/19954/energy/Charcoal-Gasification He wrote a fair amount here on permies on the subject and may be well along on his own project by now. Also this http://www.driveonwood.com/ is an excellent resource, many people who convert their vehicles end up going the route of charcoal gasification for the simplicity and energy densification (less volume of fuel to carry) that approach provides.

Oh yeah i stumbled across this kit charcoal gasifier a while ago that looked interest too http://www.offgridpro.com/

Thanks for the links Marcos and Dale, I did some digging and found a helpful reference catalog.

For the system flows i have in mind a 1/2" eductor http://www.clarkreliance.com/site/applications/DocumentLibraryManager/upload/e-200-1.pdf should work. Having a more difficult time determining efficiency though. According to the linked document I found eductor efficiencies as high as 8% (calculated using 150psig saturate steam as motive force while exhuasting against 30 ft of head). With a carnot limit efficiency at that temp of 36%, that is 22% of carnot efficiency. Not good but not terrible.

What i really wonder is if that efficiency ratio holds while going to higher temps and motive steam pressures, the manufacturers don't make eductors for higher temps and pressures, presumably because waste steam is most often used and no one wastes high quality steam on eductors, however if it held you could conceivably exceed conventional steam engine efficiencies with a far simpler system. Say 1010 deg F (or higher since fatigue and failure are of little concern in this application) @ 22% carnot efficiency you'd be around 14% eductor efficiency, @ 80% micro turbine that would be 11% electrical efficiency. That is all speculation though as i really can't find anything on eductor efficiency other than manufacturers stated performance numbers at those low temps. My hunch is that the efficiency ratio declines though as temp and pressures increase. Still i'd like to figure out how to properly model the situation. For small scale systems this might be a pretty workeable route to go.



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Steam powered eductors are a simple, though less efficient way to pump water http://en.wikipedia.org/wiki/Injector . They were first used as a boiler feed pump on a steam locomotive. Their disadvantage over mechanical modes of pumping is low efficiency.

I am curious though as to whether they could be used effectively in an integrated micro pumped storage energy system. The specific application i had in mind is an aquaponic system where exhausted hydroponic water is needed to circulate to a clean upper level reservoir. This reservoir could be oversized and placed at a higher head elevation and used as both a clean water reservoir for aquaculture make-up and also as a small micro-hydro storage system. Steam to power the eductor could be generated through one or a combination of bio-gas, solar and biomass resources. The system could be designed with nearly no moving mechanical parts (use an eductor for the boiler feepump).

I haven't got a good handle on what the efficiency would end up being, but know for the electrical generation component it would be low. However the mechanical simplicity and potential to integrate the wasted energy into other functions could make it an attractive overall system for certain off grid applications, particularly for northern climates where alot of heat is going to have to go into the operation to keep it running during the winter months. There the eductor would basically serve a dual purpose of pumping and warming the water as well as providing a small amount of electricity for other system operations. Any thoughts or feedback on the idea ?

Nice find Marcos! This system looks very promising, for starters distributed solar thermal systems of that scale will prove to be more efficient overall (once line losses and other complexities are factored in), the choice of a steam engine at that scale is also wise, in fact i'd argue that the steam engine is the only engine of choice for solar thermal since temperatures above 600 deg F become prohibitively expensive to generate and increase overall costs of solar collector. As you mention steam turbines only shine at high steady state power outputs, to which i'd also add high temps preferably of 1000 deg F +- 10 deg to the list. Part of the reason steam turbines evolved as the dominant heat engine for power generation was their ability to operate at higher temps and therefore higher efficiencies since lubrication was a non issue whereas there piston counterpart suffered above 600 deg F.

I think your ideas of using this concentrated energy for cooling and water distillation are a fascinating potential for hot areas with high cooling loads and high solar insolation. The system would act as a very effective electrical energy use displacer and would reduce electrical needs to some LEDs and and communication/power electronics at which point a very small PV system could cover it. One the best things about the system is that you could almost close the loop on a home water cycle. Since this system would likely be targeted for the off grider in the southwest my next question would be how to best integrate it into an aquaponic system?

Marcos,
Have you ever considered running a stirling engine as a cooler or even simpler an open loop single piston expansion cooler with air as working medium? I've not looked into the realities of it, but seems conceptually simple enough. Probably need to run multiple stages to achieve desired cooling temp, but don't see why it couldn't be done with a slow speed high volume simple to construct approach. Any thoughts on the idea?

Marcos,
Did you contact Mark Norton too, he was project manager for a while there and did considerable design and research on the project and may have some missing pieces to your project... I recall hearing that two stroke diesel converted to a "bump" valve was problematic from a longevity standpoint, though even if that was the case it is probably nothing that couldn't be resolved through basic design material choice changes.

I agree with the idea of compromising efficiency through elimination of regen to lower project costs and complexity, using high temp exhaust to drive a chiller and water distillation processes is pretty genius too if you have the need for it. I hope you share the system you end up going with here.


One more crazy steam idea; Have you ever heard of Frank Schuman, a turn of the century solar energy inventor? He used solar energy at 200 deg to drive a subatmospheric steam cycle. The efficiences were obviously low 50% or so of maximum carnot, but it worked https://groups.google.com/forum/#!msg/publicintel/SKrFkbrQOJk/P-U3DJbyZxUJ Anyways i thought that a really novel cycle would be to use low temp solar energy to provide heat of vaporization in such a sub atmospheric cycle and then superheat it with combustible fuel to get high efficiencies. Depending on degree of superheat the energy input would be something like 60-70% low cost solar and 40-30% combustible fuel source. It'd of course require a large condenser to maintain such low temps, and the engine would be extremely high volume due to the low pressure diff, but one advantage is that it'd be an inherently safe cycle since its less than atmospheric pressure.

Marcos Buenijo wrote:

I think Nick sees some of my perspectives. One less level of support is also what I see along with increased energy security for individuals (due to the long term storage qualities of high grade coal). Nick is spot on with his characterizing the utilities as monopolies (quite literally this is the case). I believe the energy system in place with the enormous central power stations and national grid is a Frankenstein that would never had developed without the force and fraud facilitated by government (the source of monopoly). The steady degradation of the national grid is testament to its unnatural state. It was ill-conceived by central planners who accessed the resources of the people through institutionalized fraud and theft (credit expansion, partial legislation, subsidies, etc). It's been said that such "grand" public works could never be built without government intervention - well, maybe projects that require the force and fraud of governments should not be pursued.

The two social institutions that have the most influence are language and money. Both developed organically. Today, both are manipulated by the unscrupulous to perpetuate fraud. In particular, I find the manipulation of money to be the most pernicious, but it was the false promises of politicians that facilitated this. The vast majority do not understand the following, but it's quite accurate to state that money has ceased to exist. What we have today is currency that no longer has any ties to money. As long as this condition persists, then those who control the currency will have access to the resources. It will continue as long as we continue to give value to their currency by using it for long term savings, or saving financial instruments denominated in their currency. The system in place has degraded to the point where it's increasingly difficult to make significant gains in personal wealth that do not come at the expense of others. I think many understand this on an intuitive level, and this drives a desire to drop out of a system seen as "unsustainable", or just plain malicious and destructive.

I see nothing wrong with an individual making use of fossil fuels. However, this does not mean I support how fossil fuels are used today. I ask the readers to consider that fossil fuels may not be a problem so much as the central control of these resources.

I agree with your stance on centralization of power as being the dominant corrupted influence on how fossil fuels are used. There is no inherent reason the grid should have developed that way, it was pushed and forced that direction. It is actually more efficient in most cases to transport the energy via rail then via grid, line losses are significant and per mile BTU losses are less via rail. Many problems we are having with even pollution would be resolvable on a decentralized level. Coal is of course fossilized plant material, the level of heavy metals it contains is typical of what ambient ground conditions are in that area. If coal was burnt in a decentralized manner and scrubbed with algae systems, biochar containing ambient level of heavy metals could be produced and cycled into the soil with no increase in heavy metals to the air or soil. The pollution from coal is a result of not capturing and redistributing naturally occuring levels of heavy metals in the soil. This could be done efficiently if coal was used to produce electricty in a distributed manner and then the flue gas was captured using algae to produce biochar. The biochar would pose no problems to the soil as it would have very similar distributions of heavy metals to what is already occuring. It can't occur though on a centralized system because the centralized plant is paying both an inefficient electrical line loss and then a very significant redistribution penalty. This means that those heavy metals go airborne and bioaccumulate in the aquatic ecosystems, instead of being placed back in the soil in naturally occuring concentrations.

If coal was burned in a decentralized manner and CO2 was sequestered in biochar derived from algae we'd have a near carbon nuetral energy source and would effectively redistribute all the ancient organic matter that went into production of coal in the upper levels of the soil where it could help develop better soil. Coal could be used as a powerful tool to transform overall soil fertility planet wide, by basically burning old algae for energy and using waste streams to produce algae derived biochar. Sounds crazy to most people who have been instinctively brainwashed into thinking fossil fuels=BAD, but it is IMO a legit possibility, at least from a technical feasibility standpoint.

Anyways i get what you are trying to do on a small scale Marcos with your simple steam coal powered energy system and think it sounds like a realistic approach. I researched a similar system for open source ecology some years ago, here http://opensourceecology.org/wiki/File:Integrated_Energy_System.jpeg is a system I found that was designed by Skip Goebel that seemed to me to be a good approach. Might consider contacting him, though i think he might be an expat by now. If i didn't happen to be one of the millions of brainwashed recently indebted college grads and had some finances or a decent job i'd probably be looking into doing exactly what you are doing.

Cj Verde wrote:

Marcos Buenijo wrote:Personally, I prefer to see as many people as possible become self-reliant to increasingly strip power away from the monolith that I see as the source of most of our problems. The cards are stacked against those who wish to try, so I say use whatever resources are available.

I agree with Nick and it's hard to reconcile your statement above with your interest in coal.

If you don't have coal on your property, then you're giving money to the monolith and remaining dependent of them.

I think giving money directly to coal miners and mining operations is one less level of support of the monolith than paying the utility for their services. The utilities are a mandated centralized monopoly and are just one such class of centralized mandates. The idea here i think is to fight fire with fire so to speak and use their point of leverage (low cost dirt cheap coal) to beat them at their own power game.

The problem is we are all forced into a dog eat dog competitive economic environment and an essential aspect of succeeding in the environment is having a high EROEI energy source on your side. You can not be economically viable if your net energy gain is too low. The use of high EROEI has allowed for oil and iron to displace and outcompete nearly every small family farm in the country. The resurgence of small "sustainable" farms is made possible only by an indirect energy subsidy in the form of well off consumers who earned there money from the fossil powered industrial system. We are all at root dependent on optimizing the highest EROEI fuels out there because our financial system imposes a mandate of maximizing return on investment. Permaculture will never take off at any broad level under the current economic growth mandated imperative unless it can produce higher net yields than current system. In a fossil free environment of course a closed loop symbiotic system such as those employed by permaculture designers would win, but at present every one is directly or indrectly utilizing high EROEI fuel sources to be economically viable. So perhaps it may be necessary to temporarily capitalize on high EROEI fuels just to get a foothold for the future non fossil powered world.

Going back to the topic of coal I wanted to share an idea for a community scale integrated coal system that might be viable.
A gasifer powers a 100kW-1MW scale industrial natural gas IC genset. Waste heat is utilized in adjacent greenhouse and nearby homes. A closed loop algae system scrubs 50-80% of CO2. Algae is pressed for liquid fuel and remaining biomass is composted to help with the generation of soil. The coal powered engine acts essentially as a nucleus to speed up the overall biomass production and ensure year round photosynthetic activity. The waste heat of the system can accomplish numerous functions that are not possible in the highly centralized system, home heating greenhouse heating, and water purification all come to mind. The whole operation could also be run on biomass, (or natural gas) should the availability or need arise, thus giving it a significant edge in resiliency, but in the mean time it could leverage the low coal costs to provide a financially viable way for a community to get out from under the thumb of the utility and take the power back to a much more regional level.
I haven't put any real numbers to the cost of such a system, but without even including the symbiotic stacking effects of the greenhouse, waste heat ect the capital costs of an engine at $500/kW for a 20,000hr long lasting engine and coal at $3/million BTU and a heat rate of say 10,000BTU/kWhr for rough easy figuring yields costs of $.055/kWhr, operation and maintenance costs would be very scale sensitive though and would need to be offset by the additional products that the waste heat is able to produce, but should still be able to occur at or below the utility level of $.12/kWhr. The utility may have an efficient centralized station and and more efficient means of getting access to coal but losses much in the way of not integrating waste heat losses and also has become extremely bloated with bureaucratic hiearchy costs. A integrated distributed coal system could out-compete the utility in certain situations on account of those inefficiencies if it could work around the mandated monopoly the utility has imposed. Of course that would be the type of thing that could only be done if it was decided that its imperative to decouple from the centralized monolith system and hedge bets.